The present invention relates to the field of voice and data communications, and in particular, a method and apparatus for coupling a voiceband modem circuit to a common phoneline connector for use in a home network communications system.
Referring to FIGS. 1a-1e, an evolution of home based communications systems is depicted.
In FIG. 1a, plain old telephone service (POTS) wiring 102, generally unshielded twisted pair (UTP) wiring, at customer premises 104 couples POTS telephones 106 through subscriber loop 108 to a telephone company central office, which, in turn, is connected to the public switched telephone network (PSTN). Customer premises 104 is a telephone subscriber site that has arranged (generally for a monthly telephone service fee or for a per call minute fee) with a local provider (such as a local telephone company) for a connection to the central office. The central telephone office (also called a local exchange) provides local switching and non-local switching via the PSTN.
In FIG. 1b, computer 110 through conventional voice modem 112 can also be coupled to POTS wiring 102 to allow the transmission of signals from computer 110 to be transmitted onto the telephone network. Voice modem 112 will be described in more detail below.
In FIG. 1c, there is depicted a conventional local area network (LAN) 114 (such as an ethernet network using coaxial cable) installed at customer premises 104 in addition to any POTS wiring 102 that may be in place to connect, for example, computer 110 with computer 110a. 
In FIG. 1d, computers 110 and 110a, rather than being connected via LAN 114 as seen in FIG. 1c, connects and utilizes POTS wiring 102 as a LAN transmission medium in accordance with the Home Phoneline Network Alliance (HPNA) specifications for the LAN computer interconnection over existing telephone lines within the local environment.
In FIG. 1e, computer 110, while implementing an HPNA LAN via POTS wiring 102, can also implement broadband digital data services through digital subscriber line (XDSL) modem 116, including one which supports asymmetrical digital subscriber line (ADSL) protocol, coupled to POTS wiring 102.
While broadband data services using DSL, or similarly cable modem or fixed wireless transceivers, are now being regularly deployed in home environments, there is still a need for basic connectivity using legacy voiceband data modems. Moreover, in the case of DSL and particularly ADSL, the broadband service may use the same physical metallic pair over which the voiceband modem signals travel to the PSTN central office, though at higher frequencies. In many cases, there may be no splitter (low-pass filter) between the in-premise wiring and the local loop.
Therefore, a need exists for a method and apparatus for attenuating high-frequency interfering signals, such as splitterless ADSL or phoneline network signals, at the front-end of a voiceband modem. The present invention provides a solution to this problem and will enable low-cost voiceband modems which use line-powered DAAs to be able to effectively connect to the PSTN.
In accordance with the present invention a method and apparatus for coupling a voiceband modem circuit to a common phoneline connector is provided, the common phoneline connection having a ring line connection and a tip line connection which couples a ring/tip line pair to a subscriber loop circuit, the voiceband modem circuit operating in a voiceband modem operating frequency band and having a voiceband modem interface ring line and a voiceband modem interface tip line.
In particular, in one embodiment of the present invention the voiceband modem interface ring line is coupled to the ring line and the voiceband modem interface tip line is coupled to the tip line connection by inserting, between the ring line connection and the voiceband modem interface ring line and between the tip line connection and the voiceband modem interface tip line, a series pair of inductors. A first inductor of the series pair has a low inductance and a high self-resonant frequency and a second inductor of the series pair has a high inductance and low self-resonant frequency. The low inductance, the high self-resonant frequency, the high inductance and the low self-resonant frequency are each determined to locate a filtering cutoff point between the voiceband modem operating frequency band and a digital subscriber line operating frequency band.
In another embodiment a method and apparatus for coupling a voiceband modem circuit and a digital subscriber line circuit to a common phoneline connector is provided, the common phoneline connection having a ring line connection and a tip line connection which couples a ring/tip line pair to a subscriber loop circuit, the voiceband modem circuit operating in a voiceband modem operating frequency band and having a voiceband modem interface ring line and a voiceband modem interface tip line, the digital subscriber line circuit operating in a digital subscriber line operating frequency band and having a digital subscriber line interface ring line and a digital subscriber line interface tip line. The voiceband modem interface ring line and the digital subscriber interface ring line are coupled in parallel to the ring line. The voiceband modem interface tip line and the digital subscriber interface tip line are coupled in parallel to the tip line connection. The coupling the voiceband modem interface ring line and the coupling the voiceband modem interface tip line is by inserting, between the ring line connection and the voiceband modem interface ring line and between the tip line connection and the voiceband modem interface tip line, a series pair of inductors. A first inductor of the series pair has a low inductance and a high self-resonant frequency and a second inductor of the series pair has a high inductance and low self-resonant frequency. The low inductance, the high self-resonant frequency, the high inductance and the low self-resonant frequency are each determined to locate a filtering cutoff point between the voiceband modem operating frequency band and the digital subscriber line operating frequency band.
In still another embodiment a method and apparatus for coupling a voiceband modem circuit and a home phoneline circuit to a common phoneline connector is provided, the common phoneline connection having a ring line connection and a tip line connection which couples a ring/tip line pair to a subscriber loop circuit, the voiceband modem circuit operating in a voiceband modem operating frequency band and having a voiceband modem interface ring line and a voiceband modem interface tip line, the home phoneline circuit operating in a home phone line operating frequency band and having a home phoneline interface ring line and a home phoneline interface tip line. The voiceband modem interface ring line and the home phoneline interface ring line are coupled in parallel to the ring line. The voiceband modem interface tip line and the home phoneline interface tip line are coupled in parallel to the tip line connection. The coupling the voiceband modem interface ring line and the coupling the voiceband modem interface tip line is by inserting, between the ring line connection and the voiceband modem interface ring line and between the tip line connection and the voiceband modem interface tip line, a series pair of inductors. A first inductor of the series pair has a low inductance and a high self-resonant frequency and a second inductor of the series pair has a high inductance and low self-resonant frequency. The low inductance, the high self-resonant frequency, the high inductance and the low self-resonant frequency being each determined to locate a filtering cutoff point between the voiceband modem operating frequency band and the home phoneline operating frequency band.
In yet still another embodiment a method and apparatus for coupling a voiceband modem circuit, a digital subscriber line circuit and a home phoneline circuit to a common phoneline connector is provided, the common phoneline connection having a ring line connection and a tip line connection which couples a ring/tip line pair to a subscriber loop circuit, the voiceband modem circuit operating in a voiceband modem operating frequency band and having a voiceband modem interface ring line and a voiceband modem interface tip line, the digital subscriber line circuit operating in a digital subscriber line operating frequency band and having a digital subscriber line interface ring line and a digital subscriber line interface tip line, the home phoneline circuit operating in a home phoneline operating frequency band and having a home phoneline interface ring line and a home phoneline interface tip line. The voiceband modem interface ring line, the digital subscriber interface ring line and the home phoneline interface ring line are coupled in parallel to the ring line. The voiceband modem interface tip line, the digital subscriber interface tip line, and the home phoneline interface tip line being coupled in parallel to the tip line connection. The coupling the voiceband modem interface ring line, the digital subscriber interface ring line and the home phoneline interface ring line and the coupling the voiceband modem interface tip line, the digital subscriber interface tip line and the home phoneline interface tip line is by inserting, between the ring line connection and the voiceband modem interface ring line and between the tip line connection and the voiceband modem interface tip line, a series pair of inductors. A first inductor of the series pair has a low inductance and a high self-resonant frequency and a second inductor of the series pair has a high inductance and low self-resonant frequency. The low inductance, the high self-resonant frequency, the high inductance and the low self-resonant frequency are each determined to locate a filtering cutoff point between the voiceband modem operating frequency band and the digital subscriber line operating frequency band.